fix: simplify pr.number extraction

Author: daniel-mohedano

dd-java-agent/agent-ci-visibility/src/main/java/datadog/trace/civisibility/ci/GithubActionsInfo.java

@@ -123,9 +123,9 @@ public PullRequestInfo buildPullRequestInfo() {
           baseSha = (String) base.get("sha");
         }
 
-        Object number = pullRequest.get("number");
-        if (number instanceof Number) {
-          prNumber = String.valueOf(((Number) number).intValue());
+        Double number = (Double) pullRequest.get("number");
+        if (number != null) {
+          prNumber = String.valueOf(number.intValue());
         }
       }